CODEWITHSUNDEEP
javaopengl3dlwjgl
Carl Koppa
Carl Koppa

Reputation: 41

Getting object coordinates from camera

I've implemented a camera in Java using a position vector and three direction vectors so I can use gluLookAt(); moving around in `ghost mode' works fine enough, but I want to add collision detection. I can't seem to figure out how to transform my position vector to coordinates in which OpenGL draws my objects.

A rough sketch of my drawing loop is this:

glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glLoadIdentity();
camera.setView();
drawer.drawTheScene();

I'm at a loss of how to proceed; looking at the ModelView matrix between calls and my position vector, I haven't found any kind of correlation.

Upvotes: 2

Views: 980

Answers (1)

Carl Koppa
Carl Koppa

Reputation: 41

Finally figured it out by reviewing http://fly.cc.fer.hr/~unreal/theredbook/chapter03.html again. To get from eye space (camera) to object space, you have to multiply that vector with the inverse of the ModelView matrix, or in code:

Vector4f vpos = new Vector4f(0, 0, 0, 1); 
// (0,0,0,1) because it's relative to the cam
float mv[]=new float[16];
ByteBuffer temp = ByteBuffer.allocateDirect(64);
temp.order(ByteOrder.nativeOrder());
GL11.glGetFloat(GL11.GL_MODELVIEW_MATRIX, (FloatBuffer)temp.asFloatBuffer());
temp.asFloatBuffer().get(mv);
Matrix4f m4 = new Matrix4f();
m4.load((FloatBuffer)temp.asFloatBuffer());
m4.invert();
vpos = Matrix4f.transform(m4, vpos, vpos);

Upvotes: 2

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